An IP layer handoff is the process during which the routing responsibility of a mobile node is handed over between designated mobility agents or access routers. In order to perform the handoff, a set of procedures must be executed as the mobile node moves from one access network or wireless cell to another. In order to provide uninterrupted services and continuous communication (e.g.—IP telephony), the performance of a handoff has to be evaluated with regard to short handoff interruption times and low packet loss rates.
In mobile-IP networks a mobile node can perform IP-layer handoffs between foreign agent subnets. Sometimes, the latency involved in these handoffs can be above the threshold required for the support of delay-sensitive or real-time applications. As such, a need exists for methods of achieving low-latency Mobile IP handoffs. Low-latency Mobile IP handoffs allow greater support for real-time services on a mobile access network by minimizing the period of service disruption caused by the delay in the Mobile IP registration process.
In Mobile IPv4 (IETF RFC 2002), two methods have been proposed to achieve low-latency Mobile IP handoffs under the scope of IETF Mobile IP Working Group, which are defined as Pre-Registration and Post Registration Handoffs. In the Pre-Registration handoff method, the mobile node is involved in the expected IP-layer handoff procedure. The network assists the mobile node in performing-an expected layer three (L3) handoff before it completes the corresponding layer two (L2) handoff by providing a special L2 signal known as L2 trigger.
The Post Registration handoff method proposes extensions to the Mobile IP protocol to allow the old foreign agent and new foreign agent to use information from L2 to set up bi-directional tunnels prior to the full Mobile IP registration process from the mobile node. Thus, a formal Mobile IP registration at the new point of attachment is postponed until the movement of the mobile node has completed. Bi-directional tunneling provides a fast establishment of service at the new point of attachment so that the effect of the handoff on real-time applications is minimized. However, the mobile node must still perform a formal mobile-IP registration with the foreign agent or a renewal of bi-directional tunnel sometime later.
The low latency Mobile IPv4 handoff methods propose handoff schemes where L3 handoffs are controlled or initiated by either a mobile node or an access network. Both of these schemes are founded on the hypothesis that the L3 handoff is initiated before the L2 handoff begins by utilizing L2 triggers. Both of these schemes are silent about how to initiate the L3 handoff before the L2 handoff begins. In other words, methods to achieve L2 trigger requirement are considered specific implementation issues that should stay out of working scope of the low latency Mobile IP. As such, a need exists for a method of providing a low latency handoff that initiates the L3 handoff before the L2 handoff begins.